Charge control resin particles and toner for developing electrostatic images

ABSTRACT

Charge control resin particles comprising a mixture of at least a charge control agent and a resin, wherein a crystalline zinc 3,5-di-tert-butylsalicylate represented by General Formula below, and having major peaks of X-ray diffraction using the CuK α-characteristic X-ray at Bragg angles 2θ of at least 6.4±0.2° and 15.4±0.2°, is contained as said charge control agent. Toner for developing electrostatic images which comprises a coloring agent, a binder resin for toner, and the charge control resin particles.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a toner for developingelectrostatic images permitting the control of the charge amount of atoner used to develop electrostatic latent images in electrophotography,electrostatic recording, electrostatic printing and others, and chargecontrol resin particles used as a raw material for the production of thesame toner.

[0003] 2. Description of the Prior Art

[0004] In copying machines and other equipment based onelectrophotography, various dry or wet toners containing a coloringagent, a fixing resin and other substances are used to visualize theelectrostatic latent image formed on the photoreceptor having aphotosensitive layer containing an inorganic or organic photoconductivesubstance. The chargeability of such toners is the most important factorin electrostatic latent image developing systems. Thus, to appropriatelycontrol the charge amount of toner, a charge control agent providing apositive or negative charge is often added to the toner.

[0005] Charge control agents providing a positive charge for toner inactual application include the nigrosine dyes disclosed in JapanesePatent Examined Publication No. SHO41-2427 and elsewhere. Charge controlagents providing a negative charge for toner in actual applicationinclude the metal complex dyes disclosed in Japanese Patent ExaminedPublication Nos. SHO41-20153, SHO43-17955, SHO45-26478 and elsewhere.However, most of the charge control agents described above arestructurally complex and unstable; for example, they are likely to bedecomposed or deteriorated to lose their initial charge controlperformance when exposed to mechanical friction or impact, temperatureor humidity changes, electric impact, light irradiation, etc. Also, manyof such conventional charge control agents are colored so that they areunsuitable for use in full-color toners.

[0006] As a means for resolving these problems, Japanese PatentLaid-Open No. SHO62-145255, for example, discloses the containment of ametal salt of salicylic acid or a derivative thereof as a charge controlagent. Japanese Patent Laid-Open No. SHO63-163374 proposes methods fordetermining the crystalline structures and crystalline diameters ofmetal salts of salicylic acid and derivatives thereof to be contained inthe toner, with particular mention of zinc 3,5-di-tert-butylsalicylate.Although these substances are advantageous in that they can be used incolor toners, their heat stability, uniform dispersibility in resin, orcharge control performance, or charging rise speed, in particular, isinsufficient so that they remain to be investigated further.

[0007] The present invention was developed in view of the aforementionedproblems in the prior art and is intended to provide a toner fordeveloping electrostatic images wherein the charge control agentcontained therein possesses good heat resistance, good affinity forresin and good dispersibility in resin, which exhibits a high speed ofcharging rise, which is excellent in charge stability to temperature andhumidity changes (environmental resistance) and charge characteristicstability over time (storage stability), and which can be used invarious chromatic or achromatic toners, and charge control resinparticles used as a starting material for the production of said toner.

SUMMARY OF THE INVENTION

[0008] Resolving the above problems, the charge control resin particlesof the present invention are charge control resin particles comprisingat least a charge control agent and a resin, wherein the charge controlagent contained therein is

[0009] [A] a crystalline zinc 3,5-di-tert-butylsalicylate represented byGeneral Formula (1) below, and having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray (wavelength 1.541 Å) at Braggangles 2θ of at least 6.4±0.2° and 15.4±0.2°

[0010] [B] a crystalline zinc 3,5-di-tert-butylsalicylate represented byGeneral Formula (1) below, and having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray (wavelength 1.541 Å) at Braggangles 2θ of at least 7.7±0.2° and 15.7±0.2°.

[0011] in Formula (1), t-Bu represents a tert-butyl group.

[0012] When preparing a toner for developing electrostatic images usingthe charge control resin particles of the present invention, a coloringagent and a binder resin for toner, the crystalline zinc3,5-di-tert-butylsalicylate contained in the charge control resinparticles is highly uniformly dispersed in the resin so that its chargecontrol performance is improved. In particular, reverse charging in theinitial stage of the frictional charging of the toner and chargevariation over time can be prevented.

[0013] The toner of the present invention for developing electrostaticimages, which comprises the charge control resin particles of thepresent invention, a coloring agent and a binder resin for toner, is atoner wherein the charge control agent contained therein possesses goodheat resistance, good affinity for resin and good dispersibility inresin and ensures a high speed of charging rise, it is highly effectivein increasing the speed in electrophotographic and other processes andimproving the quality of initial images thereof, is excellent in chargestability to temperature and humidity changes (environmental resistance)and charge characteristic stability over time (storage stability), andcan be used in various chromatic or achromatic toners.

[0014] The aforementioned zinc 3,5-di-tert-butylsalicylate can beprepared by providing zinc to the starting material3,5-di-tert-butylsalicylic acid obtained by butylation of salicylicacid.

[0015] If the 3,5-di-tert-butylsalicylic acid is provided with zinc by areaction in an aqueous system, the crystalline zinc3,5-di-tert-butylsalicylate of [A] above can be obtained by steps [1] to[4] below. Although it can also be obtained by a reaction using anorganic solvent system, an aqueous reaction is preferred from theviewpoint of cost and safety.

[0016] [1] Step for dissolving 3,5-di-tert-butylsalicylic acid in analkaline aqueous solution.

[0017] [2] Step for dissolving a zinc provider in water.

[0018] [3] Reaction step wherein the aqueous solution of a zinc providerobtained in step [2] is added to the aqueous solution of3,5-di-tert-butylsalicylic acid obtained in step [1], while heating thelatter, and the mixture is stirred with heating until the reaction iscompleted.

[0019] [4] Post-treatment step for filtering the reaction mixtureobtained in step [3] and washing, drying and then milling the cakefiltered off.

[0020] Specifically, the desired product can, for example, besynthesized by the following method. A sufficient amount of an alkalineaqueous solution is added to 2 mol of 3,5-di-tert-butylsalicylic acidand dissolved with heating. Separately, an aqueous solutionincorporating 1 mol of a zinc provider is prepared. This solution isadded drop by drop to the aforementioned aqueous solution of3,5-di-tert-butylsalicylic acid, while heating the latter aqueoussolution, to cause the reaction with heating and pH adjustment; aftercompletion of the reaction, the reaction mixture is filtered and thecake filtered off is washed with water and dried.

[0021] Examples of zinc providers used to provide zinc to3,5-di-tert-butylsalicylic acid include, but are not limited to, zincsulfate, zinc chloride and zinc acetate and so on.

[0022] As preferable examples of the crystalline zinc3,5-di-tert-butylsalicylate of [A] above which can be obtained by thesesteps, there may be mentioned

[0023] a crystalline zinc 3,5-di-tert-butylsalicylate having major peaksof X-ray diffraction using the CuKα-characteristic X-ray at Bragg angles20 of at least 5.7±0.2°, 6.4±0.2° and 15.4±0.2°; and

[0024] a crystalline zinc 3,5-di-tert-butylsalicylate having major peaksof X-ray diffraction using the CuKα-characteristic X-ray at Bragg angles20 of at least 5.2±0.2°, 5.7±0.2°, 6.4±0.2°, 6.7±0.2° and 15.4±0.2°.

[0025] If the zinc 3,5-di-tert-butylsalicylate is provided with zinc bya reaction in an aqueous system, the crystalline zinc3,5-di-tert-butylsalicylate of [B] above can be obtained by steps [1],[2], [3]′ and [4] wherein step [3] above is replaced with reaction step[3]′ wherein the aqueous solution of 3,5-di-tert-butylsalicylic acidobtained in step [1] is added to the aqueous solution of a zinc providerobtained in step [2], while heating the latter, and the mixture isstirred with heating until the reaction is completed.

[0026] Specifically, the desired product can, for example, besynthesized by the following method. A sufficient amount of an alkalineaqueous solution is added to 2 mol of 3,5-di-tert-butylsalicylic acidand dissolved with heating. Separately, an aqueous solutionincorporating 1 mol of a zinc provider is prepared. While heating thisaqueous solution, the aforementioned aqueous solution of3,5-di-tert-butylsalicylic acid is added drop by drop, and the reactionis carried out with heating and pH adjustment; after completion of thereaction, the reaction mixture is filtered and the cake filtered off iswashed with water and dried. As example zinc providers, there may bementioned those mentioned above.

[0027] As a preferable example of the crystalline zinc3,5-di-tert-butylsalicylate of [B] above, which can be obtained by thesesteps, there may be mentioned a crystalline zinc3,5-di-tert-butylsalicylate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray at Bragg angles 2θ of 5.2±0.2°,6.7±0.2°, 7.7±0.2° and 15.7±0.2°.

[0028] The crystalline zinc 3,5-di-tert-butylsalicylate of [B](especially that obtained by steps [1], [2], [3]′ and [4]) can beobtained as a charge control agent having a great amount of initialcharges, a good charge control characteristic, and an appropriately lowbulk density of the zinc 3,5-di-tert-butylsalicylate particles (e.g., 2to 5 ml/g). For this reason, it improves the dispersibility in resinssuch as resins for toner, making it easy to uniformly disperse in theresin, increasing the toner charging rise speed, and improving chargestability to temperature and humidity changes (environmental resistance)and charge characteristic stability over time (storage stability), andit can be transported with an increased mass per unit volume so that thetransportation cost can be reduced significantly.

[0029] The charge control agent in the present invention may consistessentially of the aforementioned crystalline zinc3,5-di-tert-butylsalicylate.

[0030] The aforementioned charge control resin particles may besolidified milled particles of a thermally kneaded product of themixture of at least a charge control agent and a resin. Such chargecontrol resin particles can, for example, be obtained by mixing a chargecontrol agent and a resin (e.g., binder resin) at a given ratio, heatingand kneading the mixture, and cooling, solidifying and milling the resincomposition thus obtained.

[0031] The mixing ratio by weight of the charge control agent (e.g.,crystalline zinc 3,5-di-tert-butylsalicylate of [A] or [B] above) andthe resin (e.g., binder resin) in the charge control resin particles ofthe present invention may preferably be 1:9 to 9:1, more preferably 3:7to 7:3.

[0032] The toner of the present invention for developing electrostaticimages is a toner for developing electrostatic images comprising theaforementioned charge control resin particles, a coloring agent and abinder resin for toner, or a toner for developing electrostatic imagescomprising a charge control agent, a coloring agent and a binder resinfor toner, wherein a crystalline zinc 3,5-di-tert-butylsalicylaterepresented by General Formula (1) above, and having major peaks ofX-ray diffraction using the CuK α-characteristic X-ray at Bragg angles2θ of at least 5.2±0.2°, 6.7±0.2°, 7.7±0.2° and 15.7±0.2°, is containedas the charge control agent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 shows an X-ray diffraction chart of the charge controlagent of Example 1.

[0034]FIG. 2 shows an X-ray diffraction chart of the charge controlagent of Example 2.

[0035]FIG. 3 shows an X-ray diffraction chart of the charge controlagent of Example 3.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Charge Control Resin Particles

[0037] Although the particle diameter of the crystalline zinc3,5-di-tert-butylsalicylate in the present invention is not subject tolimitation, it is desirable that the average particle diameter be notmore than 20 μm, preferably not more than 10 μm, from the viewpoint ofthe improvement of its dispersibility in resin.

[0038] Desired crystalline transformation for the zinc3,5-di-tert-butylsalicylate in the present invention can, for example,be achieved by wet and/or dry dispersion milling or solvent treatment.

[0039] The crystalline zinc 3,5-di-tert-butylsalicylate (charge controlagent) in the present invention surpasses conventional salicylic acidmetal salts in dispersibility in resin. When preparing the chargecontrol resin particles of the present invention by mixing thiscrystalline zinc 3,5-di-tert-butylsalicylate and a resin, and preparinga toner for developing electrostatic images by mixing the charge controlresin particles, a coloring agent and a binder resin for toner, theaforementioned crystalline zinc 3,5-di-tert-butylsalicylate in thepresent invention is more uniformly dispersed in the resin so that itscharge control performance is improved. In particular, reverse chargingin the initial stage of the frictional charging of the toner and chargevariation over time can be prevented.

[0040] Examples of resins which can be used in the charge control resinparticles of the present invention include the commonly known binderresins for toner described below. A resin preferably used in chargecontrol resin particles is a resin having a number-average molecularweight (Mn) of 2500 to 30000, preferably a resin having a weight-averagemolecular weight (Mw)/number-average molecular weight (Mn) ratio in therange from 2 to 20. The resin in charge control resin particles and theresin used to prepare a toner using the same charge control resinparticles may be identical or not.

[0041] The charge control resin particles of the present invention are,for example, produced as described below. Specifically, charge controlresin particles can be obtained by thoroughly mixing at least a chargecontrol agent and a resin in a Henschel mixer or another mechanicalmixer, and subsequently kneading the mixture in a molten state undernormal or increased pressure in a hot kneader such as a heat roll, akneader or an extruder, cooling, solidifying and then milling themixture.

[0042] The charge control agent used in the production of the chargecontrol resin particles of the present invention may, for example, be inthe form of a dry powder or a pre-drying aqueous pressed cake. Whenusing a charge control agent in a dry powder form, a dispersion aid oran additive may be added to improve its dispersibility in resin. Forexample, water or any organic solvent may be used. Specifically, afterthe charge control agent of the present invention, a resin and water orany organic solvent are mixed in a Henschel mixer or another mechanicalmixer, the mixture is charged and kneaded in a heat roll, a flasher, akneader, an extruder, or the like. Alternatively, when using a flasher,a kneader, or the like, it is possible to charge and mix the chargecontrol agent, resin and water or any organic solvent in a single stepat one time. Subsequently, the mixture is kneaded in a molten state withheating under increased or normal pressure. The remaining water orsolvent is then evaporated off under normal or reduced pressure to drythe mixture. The mixture is cooled, solidified and then milled to yieldcharge control resin particles. Although the aforementioned organicsolvent may be a commonly known organic solvent, it is preferable to usea low-boiling highly volatile solvent such as ethanol, methanol,isopropanol or acetone.

[0043] Toner for Developing Electrostatic Images

[0044] The toner of the present invention for developing electrostaticimages comprises a charge control agent [a crystalline zinc3,5-di-tert-butylsalicylate represented by General Formula (1) above,and having major peaks of X-ray diffraction using the CuKα-characteristic X-ray at Bragg angles 2θ of at least 5.2±0.2°,6.7±0.2°, 7.7±0.2° and 15.7±0.2°] or the charge control resin particlesof the present invention, a binder resin for toner and a coloring agent.

[0045] The amount of charge control agent incorporated in the toner ofthe present invention for developing electrostatic images may be 0.1 to10 parts by weight, preferably 0.5 to 5 parts by weight per 100 parts byweight of the binder resin for toner (or the sum of the binder resin fortoner and the resin in the charge control resin particles).

[0046] Examples of resins which can be used in the toner of the presentinvention include resins that have traditionally been used as binderresins for toners. Specifically, there may be mentioned synthetic resinssuch as polystyrene resin, styrene-acrylic resin, styrene-butadieneresin, styrene-maleic resin, styrene-vinyl methyl ether resin,styrene-methacrylate copolymer, polyester resin, phenol resin and epoxyresin. These resins may be used singly or in blends of several kinds. Ofthese resins, those having a glass transition point of 50 to 75° C., asoftening point of 80 to 150° C. and a number-average molecular weightof 1000 to 30000 are preferred, with greater preference given to thosewherein the weight-average molecular weight/number-average molecularweight ratio is 2 to 50.

[0047] For preferable use of a binder resin for toner and a resin incharge control resin particles in a toner used for full-color imaging bysubtractive color mixture or for OHP (overhead projectors) etc., theresin or binder resin is required to have special properties, forexample, it should be transparent, substantially colorless (no tonedamage occurs in the toner image), compatible with the charge controlagent used, fluid under appropriate heat or pressure, and pulverizable.Examples of such resins for preferable use include polystyrene resin,acrylic resin, styrene-acrylic resin, styrene-methacrylate copolymer andpolyester resin. A polyester resin or styrene-acrylic resin having anacid value of 1 to 50 mg KOH/g, in particular, is preferred.

[0048] The toner of the present invention may incorporate various knowndyes and pigments as coloring agents. Examples of such dyes or pigmentswhich can be used in color toners include carbon black, organic pigmentssuch as quinophthalone, Hansa Yellow, Rhodamine 6G Lake, quinacridone,Rose Bengale, copper Phthalocyanine Blue and copper PhthalocyanineGreen, various oil-soluble dyes or disperse dyes such as azo dyes,quinophthalone dyes, anthraquinone dyes, xanthene dyes, triphenylmethanedyes and phthalocyanine dyes, and dyes and pigments modified with higherfatty acids, synthetic resins, or the like.

[0049] The toner of the present invention for developing electrostaticimages may incorporate the aforementioned coloring agents singly or incombination. Dyes and pigments having good spectral characteristics canbe preferably used to prepare toners of the three primaries forfull-color imaging. Chromatic monocolor toners may incorporate anappropriate combination of a pigment and dye of the same color tone,such as a rhodamine pigment and dye, a quinophthalone pigment and dye,or a phthalocyanine pigment and dye, as coloring agents.

[0050] Also, to improve toner quality, additives, e.g., anti-offsetagents, fluidity-improving agents (e.g., various metal oxides such assilica, aluminum oxide and titanium oxides, magnesium fluoride, etc.)and cleaning aids (e.g., metal soaps of stearic acid etc.; varioussynthetic resin microparticles such as fluorine-series synthetic resinmicroparticles, silicone-series synthetic resin microparticles andstyrene-(meth)acrylic synthetic resin microparticles), can be addedinternally or externally.

[0051] Anti-offset agents (releasing agents) used to improve tonerfixability as described above include various waxes, particularly thosehaving average molecular weights of 500 to 15000. Specifically, therecan be used polyolefin type waxes such as low molecular polypropylene,polyethylene, oxidized polypropylene and oxidized polyethylene; andnatural waxes such as carnauba wax, rice wax and montan wax.

[0052] The toner of the present invention for developing electrostaticimages is, for example, produced as described below. A toner having anaverage particle size of 5 to 20 μm is obtained by thoroughly mixing abinder resin for toner and coloring agent a charge control agent orcharge control resin particles as described above, and, if necessary, amagnetic material, a fluidizing agent and other additives, using a ballmill or another mechanical mixer, subsequently kneading the mixture in amolten state using a hot kneader such as a heat roll, a kneader or anextruder, cooling, solidifying and then pulverizing the mixture, andclassifying the particles.

[0053] Other usable methods include the method in which the startingmaterials are dispersed in a binder resin solution and then spray dried,and the polymerizing toner production method in which a given set ofstarting materials are mixed in a monomer for binder resin to yield anemulsified suspension which is then polymerized to yield the desiredtoner (e.g., the method described in Japanese Patent Laid-Open No.HEI1-260461 and Japanese Patent Laid-Open No. HEI2-32365). When usingthe toner of the present invention as a two-component developer,development can be achieved by the two-component magnetic brushdeveloping process or another process using the toner in mixture with acarrier powder.

[0054] Any known carrier can be used. Examples of the carrier includeiron powder, nickel powder, ferrite powder and glass beads about 50 to200 μm in particle diameter, and such materials as coated with acrylatecopolymer, styrene-acrylate copolymer, silicone resin, polyamide resin,ethylene fluoride resin or the like.

[0055] When using the toner of the present invention as a one-componentdeveloper, a fine powder of a ferromagnetic material such as ironpowder, nickel powder or ferrite powder may be added and dispersed inpreparing the toner as described above. Examples of developing processeswhich can be used in this case include contact development and jumpingdevelopment.

EXAMPLES

[0056] The present invention is hereinafter described in more detail bymeans of the following examples, but these are not to be construed aslimitative on the present invention. In the description below, “part(s)by weight” are referred to as “part(s)” for short.

[0057] Examples 1 through 5 pertain to the production of charge controlresin particles.

Example 1

[0058] Polyester resin [Diacron ER561 (trade name), produced byMitsubishi Chemical Corporation] . . . 50 parts

[0059] Charge control agent (crystalline zinc3,5-di-tert-butylsalicyiate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray [wavelength 1.541 Å] at Braggangles 2θ of 5.7±0.2°, 6.4±0.2° and 15.4±0.2°; an X-ray diffractionchart shown in FIG. 1) . . . 50 parts

[0060] Methanol . . . 0.10 parts

[0061] The above ingredients were charged in a kneader and mixed for 15minutes to moisten the polyester resin powder and charge control agentwith the methanol, after which this mixture was kneaded in a moltenstate while the methanol was evaporated by gradual heating. Aftercooling, this mixture was further kneaded with a pair of heat rolls andcooled, and then roughly crushed in a vibration mill to yield chargecontrol resin particles 1.

[0062] Production of the Aforementioned Charge Control Agent

[0063] 25.0 g of 3,5-di-tert-butylsalicylic acid (0.10 mol obtained bybutylation of salicylic acid) was dissolved in 200 ml of a 2% aqueoussolution of NaOH and heated to about 70° C. Separately, 14.4 g (0.05mol) of zinc sulfate heptahydrate was dissolved in 200 ml of water. Thisaqueous solution of zinc sulfate was added drop by drop to theaforementioned aqueous solution of 3,5-di-tert-butylsalicylic acid overa period of about 30 minutes. Subsequently, after the reaction wascarried out at 70 to 80° C. for 2 hours, the reaction mixture wasadjusted to a pH of 7.0±0.5 to complete the reaction.

[0064] This reaction solution was filtered while it remained hot, andthe cake filtered off was washed with water and dried to yield 27.3 g ofa white fine powder. The bulk density of this white powder was 6.9 ml/g.Analysis of the thus-obtained white powder using a powder X-raydiffraction apparatus detected major peaks of X-ray diffraction usingthe CuK α-characteristic X-ray [wavelength 1.541 Å] at Bragg angles 2θof 5.7±0.2°, 6.4±0.2° and 15.4±0.2°.

[0065] In the present and following Examples, X-ray diffraction analysisof crystalline zinc 3,5-di-tert-butylsalicylate was conducted using theapparatus shown below on the undermentioned condition.

[0066] Instrumentation: MXP-18 X-ray diffraction apparatus (manufacturedby MAC SCIENCE K.K.)

[0067] Target: Cu

[0068] Wavelength: 1.5405 Å (CuK α 1)

[0069] Voltage and current: 40.0 kV, 200 mA

[0070] Divergence slit: 1.0°

[0071] Receiving slit: 0.30 mm

[0072] Scattering slit: 1.0°

[0073] Scanning speed: 4.0 deg/min

Example 2

[0074] Charge control resin particles 2 were prepared in the same manneras Example 1, except that the zinc 3,5-di-tert-butylsalicylate ofExample 1 was replaced with a crystalline zinc3,5-di-tert-butylsalicylate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray [wavelength 1.541 Å] at Braggangles 2θ of at least 5.2±0.2°, 5.7±0.2°, 6.4±0.2°, 6.7±0.2° and15.4±0.2° (X-ray diffraction chart shown in FIG. 2).

Example 3

[0075] Charge control resin particles 3 were prepared in the same manneras Example 1, except that the zinc 3,5-di-tert-butylsalicylate ofExample 1 was replaced with a crystalline zinc3,5-di-tert-butylsalicylate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray [wavelength 1.541 Å] at Braggangles 2θ of at least 5.2±0.2°, 6.7±0.2°, 7.7±0.2° and 15.7±0.2° (X-raydiffraction chart shown in FIG. 3).

[0076] Production of the aforementioned charge control agent 14.4 g(0.05 mol) of zinc sulfate heptahydrate was dissolved in 200 ml ofwater. Separately, 25.0 g of 3,5-di-tert-butylsalicylic acid (0.10 molobtained by butylation of salicylic acid) was dissolved in 200 ml of a2% aqueous solution of NaOH and heated to about 70° C. This aqueoussolution of 3,5-di-tert-butylsalicylic acid was added drop by drop tothe aforementioned aqueous solution of zinc sulfate over a period ofabout 30 minutes. Subsequently, after the reaction was carried out at 70to 80° C. for 2 hours, the reaction mixture was adjusted to a pH of7.0±0.5 to complete the reaction.

[0077] This reaction solution was filtered while it remained hot, andthe cake filtered off was washed with water and dried to yield 27.5 g ofa white fine powder. The bulk density of this white powder was 3.0 ml/g.Analysis of the thus-obtained white powder using a powder X-raydiffraction apparatus detected major peaks of X-ray diffraction usingthe CuK α-characteristic X-ray [wavelength 1.541 Å] at Bragg angles 2θof 5.2±0.2°, 6.7±0.2°, 7.7±0.2° and 15.7±0.2°.

Example 4

[0078] Styrene-acrylic copolymer resin [ALMATEX CPR600B (trade name),produced by Mitsui Chemicals, Inc.] . . . 70 parts

[0079] Charge control agent (crystalline zinc3,5-di-tert-butylsalicylate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray [wavelength 1.541 Å] at Braggangles 2θ of 5.7±0.2°, 6.4±0.2° and 15.4±0.2°) . . . 30 parts

[0080] The above ingredients were uniformly pre-mixed in a Henschelmixer, after which this mixture was kneaded in a molten state using akneader. After cooling, this mixture was further kneaded with a pair ofheat rolls and cooled, and then roughly crushed in a vibration mill toyield charge control resin particles 4.

Example 5

[0081] Charge control resin particles 5 were prepared in the same manneras Example 4, except that the zinc 3,5-di-tert-butylsalicylate ofExample 4 was replaced with a crystalline zinc3,5-di-tert-butylsalicylate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray [wavelength 1.541 Å] at Braggangles 2θ of at least 5.2±0.2°, 6.7±0.2°, 7.7±0.2° and 15.7±0.2°.

[0082] Examples 6 through 10 and Comparative Example 1 pertain to tonerfor developing electrostatic images.

Example 6

[0083] Polyester resin [Diacron ER561 (trade name), produced byMitsubishi Chemical Corporation] . . . 100 parts

[0084] Carbon black [MA-100 (trade name), produced by MitsubishiChemical Corporation] . . . 6 parts

[0085] Low polymer polypropylene [Viscol 550-P (trade name), produced bySanyo Chemical Industries, Ltd.] . . . 5 parts

[0086] Charge control resin particles 1 obtained in Example 1 . . . 2parts

[0087] The above ingredients were uniformly pre-mixed using a high-speedmixer. This premix was then kneaded in a molten state using an extruder,cooled and thereafter roughly milled using a vibration mill. The roughmilling product obtained was finely pulverized using an air jet millequipped with a classifier to yield a negatively chargeable black toner10 to 20 μm in particle diameter. Five parts of this toner was admixedwith 95 parts of an iron powder carrier [TEFV 200/300 (trade name),produced by Powdertech Co., Ltd.) to yield a developer.

[0088] This developer was measured in a polyethylene bottle. This bottlewas rotated under standard conditions (20° C.-60% RH) in a ball mill ata rotation rate of 100 rpm to stir and charge the developer, and changesover time in the charge amount of the developer were determined. Theresults of the determination of changes over time in the charge amountare shown in Table 1.

[0089] Separately, this developer was measured in a polyethylene bottle.This bottle was rotated in each of a low-temperature low-humidity (5°C.-30% RH) atmosphere and a high-temperature high-humidity (35° C.-90%RH) atmosphere in a ball mill at a rotation rate of 100 rpm for 10minutes to stir and charge the developer, and changes over time in thecharge amount of the developer in each case were determined. The resultsof the determination of the environmental stability of the charge amountare shown in Table 2.

[0090] Changes Over Time in Charge Amount TABLE 1 Time (min) 1 3 5 10 1530 Charge amount (−μ C/g) 30.0 31.9 33.5 36.0 38.0 38.5

[0091] Environmental Stability TABLE 2 5° C. - 30% RH 35° C. - 90% RHCharge amount (−μ C/g) 38.2 38.0

[0092] When this developer was used to form toner images using acommercial copying machine (selenium drum type), fogging-freehigh-quality images with good thin line reproducibility and good chargestability and sustainability without image density reduction wereobtained. The offset phenomenon was never observed.

Example 7

[0093] Styrene-acrylic copolymer resin [ALMATEX CPR600B (trade name),produced by Mitsui Chemicals, Inc.] . . . 100 parts

[0094] Carbon black [MA-100 (trade name), produced by MitsubishiChemical Corporation] . . . 6 parts

[0095] Low polymer polypropylene [Viscol 550-P (trade name), produced bySanyo Chemical Industries, Ltd.] . . . 5 parts

[0096] Charge control resin particles 1 obtained in Example 1 . . . 2parts

[0097] The above ingredients were treated in the same manner as Example6 to yield a negatively chargeable black toner 10 to 20 μm in particlediameter and a developer. Using this developer, changes over time incharge amount and the environmental stability of charge amount weredetermined in the same manner as Example 6. The results are shown inTables 3 and 4, respectively.

[0098] Changes Over Time in Charge Amount TABLE 3 Time (min) 1 3 5 10 1530 Charge amount (−μ C/g) 21.5 23.3 24.1 24.7 25.0 26.5

[0099] Environmental Stability TABLE 4 5° C. - 30% RH 35° C. - 90% RHCharge amount (−μ C/g) 26.5 25.6

[0100] When this developer was used to form toner images using acommercial copying machine (selenium drum type), fogging-freehigh-quality images with good thin line reproducibility and good chargestability and sustainability without image density reduction wereobtained. The offset phenomenon was never observed.

Example 8

[0101] Polyester resin [Diacron ER561 (trade name), produced byMitsubishi Chemical Corporation] . . . 100 parts

[0102] Carbon black [MA-100 (trade name), produced by MitsubishiChemical Corporation] . . . 6 parts

[0103] Low polymer polypropylene [Viscol 550-P (trade name), produced bySanyo Chemical Industries, Ltd.] . . . 5 parts

[0104] Charge control resin particles 2 obtained in Example 2 . . . 2parts

[0105] The above ingredients were treated in the same manner as Example6 to yield a negatively chargeable black toner 10 to 20 μm in particlediameter and a developer. Using this developer, changes over time incharge amount and the environmental stability of charge amount weredetermined in the same manner as Example 6. The results are shown inTables 5 and 6, respectively.

[0106] Changes Over Time in Charge Amount TABLE 5 Time (min) 1 3 5 10 1530 Charge amount (−μ C/g) 33.2 34.5 35.6 36.9 37.5 38.0

[0107] Environmental Stability TABLE 6 5° C. - 30% RH 35° C. - 90% RHCharge amount (−μ C/g) 37.7 37.0

[0108] When this developer was used to form toner images using acommercial copying machine (selenium drum type), fogging-freehigh-quality images with good thin line reproducibility and good chargestability and sustainability without image density reduction wereobtained. The offset phenomenon was never observed.

Example 9

[0109] Polyester resin [Diacron ER561 (trade name), produced byMitsubishi Chemical Corporation] . . . 100 parts

[0110] Oil-soluble magenta dye [Oil Pink #312(trade name), produced byOrient Chemical Industries, Ltd.] . . . 6 parts

[0111] Low polymer polypropylene [Viscol 550-P (trade name), produced bySanyo Chemical Industries, Ltd.] . . . 5 parts

[0112] Charge control resin particles 3 obtained in Example 3 . . . 2parts

[0113] The above ingredients were treated in the same manner as Example6 to yield a negatively chargeable magenta toner 10 to 20 μm in particlediameter and a developer. Using this developer, changes over time incharge amount and the environmental stability of charge amount weredetermined in the same manner as Example 6. The results are shown inTables 7 and 8, respectively.

[0114] Changes Over Time in Charge Amount TABLE 7 Time (min) 1 3 5 10 1530 Charge amount (−μ C/g) 37.0 38.5 39.0 39.4 39.7 40.3

[0115] Environmental Stability TABLE 8 5° C. - 30% RH 35° C. - 90% RHCharge amount (−μ C/g) 40.2 39.8

[0116] When this developer was used to form toner images using acommercial copying machine (selenium drum type), fogging-free vividmagenta images with good thin line reproducibility, excellent spectralcharacteristics, and transparency suitable for color blending bysuperposing were obtained.

Example 10

[0117] Styrene-acrylic copolymer resin [ALMATEX CPR600B (trade name),produced by Mitsui Chemicals, Inc.] . . . 100 parts

[0118] Carbon black [MA-100 (trade name), produced by MitsubishiChemical Corporation] . . . 6 parts

[0119] Low polymer polypropylene [Viscol 550-P (trade name), produced bySanyo Chemical Industries, Ltd.] . . . 5 parts

[0120] Charge control agent (crystalline zinc3,5-di-tert-butylsalicylate having major peaks of X-ray diffractionusing the CuK α-characteristic X-ray [wavelength 1.541 Å] at Braggangles 2θ of at least 5.2±0.2°, 6.7±0.2°, 7.7±0.2° and 15.7±0.2°) . . .1 part

[0121] The above ingredients were treated in the same manner as Example6 to yield a negatively chargeable black toner 10 to 20 μm in particlediameter and a developer. Using this developer, changes over time incharge amount and the environmental stability of charge amount weredetermined in the same manner as Example 6. The results are shown inTables 9 and 10, respectively.

[0122] Changes Over Time in Charge Amount TABLE 9 Time (min) 1 3 5 10 1530 Charge amount (−μ C/g) 23.1 25.2 26.6 27.0 27.2 27.6

[0123] Environmental Stability TABLE 10 5° C. - 30% RH 35° C. - 90% RHCharge amount (−μ C/g) 27.3 26.8

[0124] When this developer was used to form toner images using acommercial copying machine (selenium drum type), fogging-freehigh-quality images with good thin line reproducibility and good chargestability and sustainability without image density reduction wereobtained. The offset phenomenon was never observed.

Comparative Example 1

[0125] A negatively chargeable black toner 10 to 20 μm in particlediameter and a developer were prepared in the same manner as Example 6,except that an aluminum compound of 3,5-di-tert-butylsalicylic acid(charge control agent) was used in place of the charge control resinparticles. Using this developer, changes over time in charge amount andthe environmental stability of charge amount were determined in the samemanner as Example 6. The results are shown in Tables 11 and 12,respectively.

[0126] Changes Over Time in Charge Amount TABLE 11 Time (min) 1 3 5 1015 30 Charge amount (−μ C/g) 22.5 26.8 29.4 32.3 33.2 35.5

[0127] Environmental Stability TABLE 12 5° C. - 30% RH 35° C. - 90% RHCharge amount (−μ C/g) 34.1 29.8

What is claimed is:
 1. A charge control resin particles comprising amixture of at least a charge control agent and a resin, wherein acrystalline zinc 3,5-di-tert-butylsalicylate represented by GeneralFormula (1) below, and having major peaks of X-ray diffraction using theCuK α-characteristic X-ray at Bragg angles 2θ of at least 6.4±0.2° and15.4±0.2°, is contained as said charge control agent.

in Formula (1), t-Bu represents a tert-butyl group.
 2. The chargecontrol resin particles of claim 1 wherein said zinc3,5-di-tert-butylsalicylate has major peaks of X-ray diffraction usingthe CuK α-characteristic X-ray at Bragg angles 2θ of at least 5.7±0.2°,6.4±0.2° and 15.4±0.2°.
 3. The charge control resin particles of claim 1wherein said zinc 3,5-di-tert-butylsalicylate has major peaks of X-raydiffraction using the CuK α-characteristic X-ray at Bragg angles 2θ ofat least 5.2±0.2°, 5.7±0.2°, 6.4±0.2°, 6.7±0.2° and 15.4±0.2°.
 4. Acharge control resin particles comprising a mixture of at least a chargecontrol agent and a resin, wherein a crystalline zinc3,5-di-tert-butylsalicylate represented by General Formula (1) below,and having major peaks of X-ray diffraction using the CuKα-characteristic X-ray at Bragg angles 2θ of at least 7.7±0.2° and15.7±0.2°, is contained as said charge control agent.

in Formula (1), t-Bu represents a tert-butyl group.
 5. The chargecontrol resin particles of claim 4 wherein said zinc3,5-di-tert-butylsalicylate has major peaks of X-ray diffraction usingthe CuK α-characteristic X-ray at Bragg angles 2θ of at least 5.2±0.2°,6.7±0.2°, 7.7±0.2° and 15.7±0.2°.
 6. The charge control resin particlesof claim 1 wherein said charge control agent consists essentially of theaforementioned crystalline zinc 3,5-di-tert-butylsalicylate.
 7. Thecharge control resin particles of claim 4 wherein said charge controlagent consists essentially of the aforementioned crystalline zinc3,5-di-tert-butylsalicylate.
 8. The charge control resin particles ofclaim 1 wherein said charge control resin particles are solidifiedmilled particles of a thermally kneaded product of the mixture of atleast said charge control agent and said resin.
 9. The charge controlresin particles of claim 4 wherein said charge control resin particlesare solidified milled particles of a thermally kneaded product of themixture of at least said charge control agent and said resin.
 10. Thecharge control resin particles of claim 1 wherein the mixing ratio byweight of the charge control agent and the resin is 1:9 to 9:1.
 11. Thecharge control resin particles of claim 4 wherein the mixing ratio byweight of the charge control agent and the resin is 1:9 to 9:1.
 12. Atoner for developing electrostatic images which comprises a coloringagent, a binder resin for toner, and charge control resin particlescomprising a mixture of at least a charge control agent and a resin,wherein a crystalline zinc 3,5-di-tert-butylsalicylate represented byGeneral Formula (1) below, and having major peaks of X-ray diffractionusing the CuKα-characteristic X-ray at Bragg angles 20 of at least6.4±0.2° and 15.4±0.2°, is contained as said charge control agent.

in Formula (1), t-Bu represents a tert-butyl group.
 13. The toner fordeveloping electrostatic images of claim 10 wherein said zinc3,5-di-tert-butylsalicylate has major peaks of X-ray diffraction usingthe CuK α-characteristic X-ray at Bragg angles 2θ of at least 5.7±0.2°,6.4±0.2° and 15.4±0.2°.
 14. The toner for developing electrostaticimages of claim 10 wherein said zinc 3,5-di-tert-butylsalicylate hasmajor peaks of X-ray diffraction using the CuK α-characteristic X-ray atBragg angles 2θ of at least 5.2±0.2°, 5.7±0.2°, 6.4±0.2°, 6.7±0.2° and15.4±0.2°.
 15. A toner for developing electrostatic images whichcomprises a coloring agent, a binder resin for toner, and charge controlresin particles comprising a mixture of at least a charge control agentand a resin, wherein a crystalline zinc 3,5-di-tert-butylsalicylaterepresented by General Formula (1) below, and having major peaks ofX-ray diffraction using the CuK α-characteristic X-ray at Bragg angles2θ of at least 7.7±0.2° and 15.7±0.2°, is contained as said chargecontrol agent.

in Formula (1), t-Bu represents a tert-butyl group.
 16. A toner fordeveloping electrostatic images comprising a charge control agent, acoloring agent and a binder resin for toner wherein a crystalline zinc3,5-di-tert-butylsalicylate represented by General Formula (1) below,and having major peaks of X-ray diffraction using the CuKα-characteristic X-ray at Bragg angles 2θ of at least 5.2±0.2°,6.7±0.2°, 7.7±0.2° and 15.7±0.2°, is contained as said charge controlagent.

in Formula (1), t-Bu represents a tert-butyl group.